1. Field of the Invention
The present invention relates to a liquid crystal display (“LCD”) device and, more particularly, to an LCD device having a reduced discharge time when an outside power is removed from the LCD device.
2. Description of the Related Art
In general, a liquid crystal display (“LCD”) is a device which displays an image by adjusting light transmissivity of liquid crystal disposed between a thin film transistor (“TFT”) substrate and a color filter substrate which have respective electrodes disposed on sides opposite to each other. The light transmissivity of the liquid crystal is controlled by an electric field generated by a voltage applied to the respective electrodes.
The LCD device includes a liquid crystal panel including a plurality of liquid crystal cells formed at intersections between data lines and gate lines, a data driver for applying a data signal voltage to the data line, a gate driver for applying a gate driving signal to the gate line, a timing controller for controlling the data driver and the gate driver, and a power supply unit for supplying a driving voltage to the liquid crystal panel.
The liquid crystal cell includes a liquid crystal capacitor in which a data signal voltage is charged and a TFT for applying the data signal voltage to the liquid crystal capacitor in response to a gate-on voltage. The driving voltage supplied from the power supply unit includes a supply voltage, a ground voltage, a gate-on voltage, a gate-off voltage, a common voltage and an analog supply voltage.
When an outside power supplied to the power supply unit is removed, the power supply unit outputs all output voltages including the supply voltage, the gate-on voltage, the gate-off voltage, the common voltage and the analog supply voltage at a ground voltage level, e.g., zero volts. When the ground voltage is applied to a gate of the TFT, the data signal voltage applied to the liquid crystal capacitor is discharged by a leakage current through a channel of the TFT.
As a result of the leakage current, a pattern displayed on the liquid crystal panel remains, even though the outside power supplied to the power supply unit has been removed, for an elapsed amount of time. The pattern slowly disappears due to the discharge by the leakage current through the channel of the TFT. The amount of time which elapses from when the outside power is removed until the pattern disappears is called a discharge time.
In the LCD device, the discharge time is determined by the leakage current which flows through the channel of the TFT when the ground voltage is applied to the gate of the TFT. Further, the discharge defect may occur at any time, due to a distribution of a threshold voltage of the TFT or an increase in the threshold voltage of the TFT due to a long driving time, for example.